Oscillating circuit



June 18,1946. F, J ALTMAN 2,402,270

OSGILLATING CIRCUIT.'

Filed March 2l, 1944 wrap/yer Patented June 18, 1946 UNETED STATES PATENT oFFicE 11 Claims.

(Granted under the act of March 3, 1883, as

The invention described herein may be manu*-` factured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to radio circui-ts and particularly circuits for producing a voltage for the deflection of a beam of a cathode ray tube.

In order to deect the beam of a cathode ray tube across the screen in a desired fashion itis common to use either magnetic or electrostatic means. In the electrostatic means deflecting plates are provided within the tube. The electron stream passing between these plates will be deflected in accordance with the potential existing across the plates. In order that the beam may sweep across the screen linearly with a quick return for the next cycle, an electrical voltage of saw-tooth wave shape is applied to the horizontal plate. Circuits for producing this saw-tooth wave shape are well known in the art.

There has recently been a growing need for a more detailed study of one portion of the guration represented on the cathode ray tube. In order to accomplish this it has been proposed that the desired portion be applied to a second cathode ray tube for expansion and more complete study. This has the disadvantage of requiring two cathode ray tubes in each system. Accordingly, it is an object of this invention to provide means to expand the desired portion on the same cathode ray tube whereon the original guration appears.

It is another object of this invention to provide a circuit for the generation of a voltage which will cause the electron beam to vary in a desired fashion as it sweeps the screen of the cathode ray tube.

A further object is to provide a circuit for altering the saw-tooth wave shape so as to vary the velocity of the electron beam sweep.

An additional object is to provide a novel means for controlling the deection of a cathode ray beam.

Other objects will be apparent from the following description and claims and reference Ato the drawing in which:

Figure l is a circuit illustrating vtlf-1e basic principles involved;

Figure 2 shows the wave shape of the voltages applied to the horizontal deecting plate'of the cathode ray tube.

Figure 3 is a complete circuit of the elementsv involved.

Reverting now in more detail to Figure l, there is shown a cathode ray tu-be 4 with a pair of amended April 30, 1928; 370 0. G. 757) horizontal deiiecting plates 5 and 6. Connected from one plate 5 to ground is capacitor 1. Across capacitor 'l there is connected a source of potential 8. The D.C voltage from source 8 is utilized to charge capacitor 'l to a desired value controlled by resistor 9 shown connected in series with source d. Also across capacitor l, directly to ground, there is shown a switching device I0. When switching device I0 is open capacitor 1 will be charged at a rate dependent upon circuit constants. 4When switching device I0 is closed capacitor l will discharge rapidly through the closed circuit.

Connected between plate 6 and ground isra'nother capacitor II. Across capacitor I I there is a source I2 of D.-C. voltage in series with resistor I3 for vcharging capacitor II in the manner explained above. Also across capacitor II directly to ground there is a switching device I4 in series with a variable resistor I5. As previously explained, capacitor II will discharge through switching device I4 when closed and charged when switch i 4 is open. However, in this circuit the rate of discharge will be slowed and controlled by resistor I5.

The potential difference across plates 5 and 6 controlling the deflection of the electron beam of cathode ray tube 4 will thus vary in accordance with the diierence of voltages applied to plate 5 andv plate 6. The circuit constants are so chosen that with switches I 0 andv I4 open the resulting charges across capacitors 'l and Il will create aA potential difference between plates .5 and 6.

' If switching device I0 is periodically opened and closed, capacitor 'I will periodically charge and discharge, thus creating a potential of sawthe voltages represented byvwave shapes I6 and Il, is shown as the resultant of these wave shapes Iand marked I B inFigure 2. Wave shape I8 in other words, depicts the difference of potentialy which eilects the shifting of the electron stream of the cathode ray tube 4.

Figure 3 is a block diagram of the componentl parts of the device. The cathode ray tube 4 contains the deflecting plates and 6. 'I'he sources oi' direct current 8 and l2 charge condensers 'l and I I through resistors 9 and I3, respectively. Adjustable resistor l5 slows down and controls the discharge of condenser Il. t The switches lndicated in Figure 1 at i0 and I4 are here shown as electronic switches. An oscillator 2i) supplies sine waves to both electronic switches. A phase shifter 2i provides that the expanded portion of the sweep may be moved anywhere with relation to the main sweep. Square wave generators 22 and 23 feed the waves to pulse Shapers 24 and 25 where the waves are shaped into short pulses which pulses cause the vacuum tubes 26 and 27 to conduct while the pulse lasts and thus provide a. path for the discharge of condensers l and ii, respectively. Batteries 28 and 29 provide bias for vacuum tubes 2t and 21.

The mode of operation of my device is believed to be obvious. 'I'he capacitors 'l and il are charged and periodically discharged each time one of the vacuum tubes 26 or 21 is rendered conducting. Since the pulses which render vacuum tubes 26 and 21 conducting originate at the same source the result is that voltages of the same frequency but differing in phase are applied to the deilecting plates 5 and 6. Due to the shape of the resulting wave, the electron beam of cathode ray tube 4 is moved at parts of its sweep or trace over the face of the tube at an increased speed. Ihis causes a portion of its path of travel to have the effect of being expanded and thus permits a. closer inspection of the4 wave figuration over this portion of the movement of the beam.

The foregoing is merely one embodiment of my invention. Other modications will readily occur to those skilled in the art. There are two important features to this invention: first, the separate use of each of a pair of deecting plates in order to apply the difference of two voltages to an electron beam; and, second, the production of an expanded sweep wherein a controlled length of main sweep may be expanded.

A small, cheaper cathode ray tube with a plate grounded to an anode may be used, the two sweep voltages being combined by connecting two resistors between the generators and obtaining the voltage from the common point.

One fact that is worthy of mention is the relationship between the retrace time of the auxiliary sweep and the length of the electronic switch pulse. It is evident that the pulse must last long enough to permit nearly complete discharge of the condenser (t=3RC, for instance) It might be desirable, for awide latitude of` control, to couple the variable resistor in series with the switch, and a pulse length control.

I claim:

1. In an oscilloscope circuit, a cathode ray tube with a pair of horizontal defiecting plates, an oscillator for .generating an alternating potential of desired frequency, a first circuit for generating impulses of the square-wave type connected to said oscillator and means for varying the phase of the output of said first circuit, a second circuit for generating impulses of the square-wave type connected to said oscillator, a first tube normally bi-ased beyond cut-01T connected to said first circuit, and -a second tube normally biased beyond cut-ofi connected to said second circuit, a first capacitor, a variable resistor connecting said rst capacitor to said first tube, means for charging said first capacitor, and a connection between said first capacitor and one of said horizontal deflecting plates, a second capacitor connected directly to said second tube, and means for charging said second capacitor, said second capacitor being connected to the second of said horizontal defiecting plates.

2. In an oscilloscope circuit, a cathode ray tube with a pair of horizontal defiecting plates, a first circuit for generating an electrical potential oi' saw-tooth wave shape and means for applying said potential to one of said horizontaldeiiecting plates, a second circuit for generating an electrical potential of saw-tooth wave shape 'and means for applying the output of said second circuit to the second of said deecting plates, means for varying the amplitude of said first potential and means for adjusting the phase of said rst potential, and an oscillator, connected to said first circuit and to said second circuit whereby the outputs of said rst circuit and said second circuit are of the same frequency.

3. In an oscilloscope circuit a cathode ray tube with a set of deecting plates, a first capacitor connected to one of said defiecting plates, and a second capacitor connected to the second of said deiiecting plates, a source of electrical potential for charging said rst and said second capacitors, switching means for periodically discharging said first capacitor, and switching means for discharging said second capacitor at the same frequency of periodic discharge as said ilrst capacitor, means for controlling the rate of discharge of said second capacitor, and means for'controlling the phase of periodic discharge of said second capacitor with respect to discharge of said rst capacitor.

4. In an oscilloscope circuit, a. cathode ray tube with apair of deiiecting plates, a source of electrical potential of saw-tooth wave shape applied to one of said deecting plates and a source of electrical potential of saw-tooth wave shape applied to the second of said deiiecting plates and means for varying the phase of said second potential, said second potential being of the same frequency as said first potential.

5. VIn an oscilloscope circuit, a cathode ray tube r, with a pair of deecting plates, means for generating an electrical potential of saw-tooth wave shape and means for applying said potential to one of said defiecting plates, means for generating a second electrical potential of saw-tooth wave shape, means for varying the amplitude of said second potential, means for varying the phase of said second potenti-a1, and means for applying said second potential to the second of said deflecting plates.

6. In an oscilloscope circuit a cathode ray tube with a set of deecting plates, a first circuit for generating an alternating electrical voltage connected to one of said deflecting plates, and a second circuit connected to the second of said deecting plates, for generating an electrical voltage of alternating frequency equal to the output frequency of said iirst circuit, means for varying the amplitude of the output of said second circuit, and means for Varying the phase of the output of said second circuit. 1

7. The method of varying the sweep velocity of a cathode ray tube which comprises periodically charging and discharging a capacitor, applying the resultant potential across said capacitor to one plate of a pair of deecting plates on said cathode ray tube, periodically charging and discharging a second capacitor and applying the resultant potential across said second capacitor to the second plate of said pair of defiecting plates, the frequency of periodic discharge of said first capacitor being equal to the frequency of periodic 5 discharge of said second capacitor, and adjusting the phase of discharge frequency of said second capacitor relative to discharge frequency of said ilrst capacitor.

8. The' method of varying the velocity of electron sweep of a. cathode ray tube which comprises generating an electrical voltage of desired frequency, utilizing a. portion ofsaid voltage to excite a rst circuit for the generation of electrical impulses, applying the output of said rst circuit to a first tube normally biased beyond cut-off whereby said irst tube conducts during the time that electrical impulses are applied theret'o, charging a iirst capacitor, discharging said rst capacitor through said rst tube during the time said rst tube is conducting, applying the potential across said irst capacitor to one of a pair of deficcting plates on said cathode ray tube, adjusting the phase of a, second portion of said alternating voltage, utilizing saidsecond portion to excite a second circuit for generating electrical impulses, applying the output of said second circuit to a second tube normally'biased beyond cutoff whereby said second tube conducts during the time that electrical impulses are applied thereto, charging a second capacitor, and discharging said second capacitor through a variable resistor and through said second tube during the time said second tube is conducting and applying the potential across said second capacitor to the second of said pair of deilecting plates.

9. The method of denecting an electron beam 6 f of a cathode ray tube which comprises applying a variable electrical potential to one plate of a pair of deiecting plates on said cathode ray tube,

ap'plying a variable electrical potential to the sec-` ond plate of said pair of deecting plates, adjusting the phase' and amplitude of the potential applied to said second plate .whereby the electron beam is deflected at a varying rate in accordance -with the varying potential across the said deflect- 1l. The method of varying the velocity Aof sweep of a cathode ray tube which comprises generating a. voltage of saw-tooth wave shape and applying said voltage to one of av pair of deecting plates in said cathode ray tube, generating a second voltage.

of saw-tooth wave shape and applying said second voltage to the second of said pair ofdeiiecting plates, adjusting the amplitude of said second voltage', and adjusting the phase of said second voltage relative to said iirst voltage.

FREDERICK J. ALTMAN. 

